Cellular telephone and smart phone handsets have within them an electro-acoustic transducer called a receiver (earpiece) that converts an input electrical audio signal into sound pressure waves that are heard by the user who is holding the handset to her ear. The receiver thus lets the user hear conversation by the other side during a wireless telephone call. Although the sensitivity of the receiver is of course a factor in how well the other side of the conversation can be heard, the manner in which the receiver is packaged inside the relatively tight confines of the handset also plays a big role.